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The Morphometrics of Box Turtles - George Patton and Martha Ann Messinger  


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Box turtles vary in size for various reasons. Turtles of the subspecies, Terrapene carolina major (Gulf Coast box turtle) are normally larger than those of the subspecies T. c. carolina (eastern box turtle) and T. c. triunguis (three-toed box turtle). The males of T. c. c. and T. c. m. are usually larger than the females of the same subspecies (Boundy 1995, Carr 1952, Dutros 1974, Nichols 1939, Prichard 1979, Stickel and Bunck 1989) . Taylor (1894) had this to say about the three-toed box turtle "The Louisiana form seems to be the dwarf variety of this species…". Our observations support Taylor as we have observed a few T. c. t. from outside Louisiana at our study site (Messinger and Patton 1995) and noticed that they were generally large than our local T. c. t..

When we weighed 129 north Louisiana three-toed box turtles we found the following: Sixty five males had a mean weight of 332 grams (range 220-449) and sixty four females had a mean weight of 435 grams (range 319-615).

For a number of years we measured wild T. c. t. using the following method. We would place the anterior edge of the carapace against a wall and measure the distance from the wall to the posterior edge of the supracaudals (#12 marginals) using a carpenter’s "T". We also measured the height of the shell at the highest point. We found that the females generally had a greater carapace length and a greater shell height.

Using that information, we determined the ratios of weight to shell height and of carapace length to shell height. The females had a greater weight per unit of carapace length and also a greater shell height per unit of carapace length. We could use either of those ratios alone to determine the sex of an adult box turtle with about 85% accuracy.

In 1998, we were able to obtain more accurate measurements of the carapace length using a Metric Caliper (300 mm Range, 63 mm jaw length with an accuracy of ± .05 mm). Measuring the length of the carapace from the anterior edge of the nuchal to the posterior of the seam between the supracaudals. The mean carapace length (m.c.l.) of 32 adult females from north Louisiana was 126.95 mm (range 118-139.1 mm). We measured eight males, using the above caliper, and got a mean carapace length of 117.5 mm.. We also extrapolated from 83 carapace measurements of other wild males and determined their m.c.l. to have been about 119 mm.. This is compatable with the m.c.l. of 117.5 mm. we found for the eight, and suggest that it is a valid figure.

Boundy (1995) measured 311 adult T. c. t. from southern Louisiana and the mean carapace length was 123 mm (range 104-147) and there was no significant difference between the sexes. He also measured 588 adult T. c. m. from southern Louisiana and found the mean carapace length to be 164.3 (range 142-191). His measurements of 395 adult T. c. m. gave a the m.c.l. of 167.3 mm. for males and 156 mm. for females.

Using data from Schwartz et al. (1984) we came up with this for three-toed box turtles in Missouri: the m.c.l. of 98 males was 123.5 mm. (range 107-140) and the m.c.l. of 82 females was 130.6 mm. (range 108-152). This indicates that the T. c. t. of Louisiana are smaller than those of Missouri. In northern Louisiana and in Missouri the female T. c. t. is larger than the male.

As the female T. c. t. is normally larger than the male, the sexual dimorphism of T. c. t. is the reverse of that of T. c. c. and T. c. m., the males of which are usually larger than the females.

Boundy, J. 1995. Status of box turtles in Louisiana. First quarterly report. Louisiana Department of Wildlife and Fisheries, baton Rouge, LA. Unpublished. 10 pp.

Carr, Archie. 1952. Handbook of Turtles. The turtles of the United States, Canada, and Baja California. Cornell Univ. Press. Ithaca, N. Y. 542 pp.

Drotos, Edward J. 1974. The box turtle: Natural history notes. Virginia Wildlife. May:7-8.

Messinger, Martha Ann & George M. Patton, 1995. Five Year Study of Nesting of Captive Terrapene carolina triunguis. Herpetological Review Vol. 26 (4) 193-195.

Nichols, J. T. 1939. Data on size, growth and age in the box turtle, Terrapene carolina. Copeia, 1939: 14-20.

Pritchard, P. C. H. 1979, Encyclopedia of turtles. T.F.H. Publications, Neptune, New Jersey.895 pp.

Schwartz, Elizabeth R., Charles W. Schwartz and A. Ross Kiester. 1984. The Three-toed Box Turtle In Central Missouri, Part II: A Nineteen Year Study Of Home Range, Movements and Population. Missouri Department of Conservation, Jefferson City, Missouri.

Stickel, Lucille f. and Christine M. Bunck. 1989. Growth and Morphometrics of the Box Turtle, Terrapene c. carolina. Journal of Herpetology 23(3):216-223.

Taylor, W. E. 1894. The box turtles of North America. Proc. U. S. Nat. Mus. No. 1019 17:573-588.  

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